Question

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Answer 1

Explanation:

Once the myosin-binding sites are exposed, and if sufficient ATP is present, myosin binds to actin to begin cross-bridge cycling. Then the sarcomere shortens and the muscle contracts. In the absence of calcium, this binding does not occur, so the presence of free calcium is an important regulator of muscle contraction.

Answer 2

Answer:

C, The myosin filaments remain in lace as they pull the actin filaments inward

Explanation:

Muscles contract when the heads on the myosin filaments latch onto the actin filaments, drawing them inward. As a result, the entire sarcomere shortens, resulting in a muscle contraction.